ZrN – bulk metallic glass composite formation under laser processing

Inga Goetz¹, Ulf Jansson¹, Jochen Schneider²

¹Uppsala University, ²RWTH Aachen University

Compositional and structural changes due to reactive species can occur both as unintentional contamination and as an intentional synthesis step. Metal additive manufacturing commonly employs an inert process gas to provide a controlled atmosphere and minimize the effects of residual oxygen or other reactive species. For Zr-based metallic glasses, oxygen impurities, present due to the raw materials or processing, have been related to loss of glass forming ability. If not seen as undesired contamination, but as a tunable printing parameter, reactive gases in laser processes may open up new possibilities. The atmosphere can be used intentionally to induce the formation of desired secondary phases. A well-known example from laser nitriding is TiN formation on Ti. In the present study, we show that by processing a Zr-based alloy (Zr59.3Cu28.8Al10.4Nb1.5, trade name AMZ4, Heraeus Holding GmbH) via direct metal laser sintering in nitrogen the formation of ZrN - metallic glass composites is achieved. The samples are printed utilizing high-purity nitrogen (N2 ≥ 99.999 %) in an EOS M100 (EOS GmbH). Incorporation of nitrogen into the layer surface is observed along with a decrease in glass forming ability throughout the build compared to processing with the same parameter settings in argon. ZrN formation occurs close to the surface of the printed layer. 
With an understanding of this process, the atmosphere could be used to form bulk metallic glass - ceramic composites and locally tailor structure and composition at specific positions within a build.